SACRAMENTO, Calif. - Among the human endeavors that call for high technology, killing weeds seems to rank in the lower strata. Yet weeds are exactly what the California Department of Transportation (CalTrans) is targeting with its latest application of technology. Department officials have leased an innovative sprayer that uses computer technology and advanced optics to determine whether a weed is present. If so, the sprayer triggers the appropriate nozzle and the weed is sprayed. If not, the machine passes over the ground without firing. The result is that only weeds are sprayed, not bare ground. The savings in chemical usage can be tremendous. That's important not only from a budgetary standpoint, but also in helping the department meet its goal of cutting chemical use by 50 percent by the year 2000 and by 80 percent by 2012, explained Larry Shields, landscape program administrator for Caltrans. "We believe we can save 40 percent of our spot treatment chemical use," he said.

Tracking Chemical Use The sprayer also ties into other aspects of the coming computer revolution in agriculture. Because the sprayer utilizes computer technology, on-board memory can be added. That means it can record chemical use data, which can be downloaded into an office computer. If Caltrans wants, it could also note the exact location of the chemical application by equipping the truck with field-mapping software and a Global Positioning System (GPS) monitor. The department leased the sprayer in June. In the first trials, the sprayer has worked as advertised. But there have been logistical problems. The sprayer is used to control weeds along state highways, and the many physical obstacles present - guardrails, signposts, etc. - mean that operators must periodically adjust the sprayer's boom. In addition, the boom's eight-foot-width makes it too long for the three-foot and five-foot strips found along some highways. Those are correctable problems, said Dale Wallander, sales representative for Los Gatos, Calif.-based Patchen California Inc., the company that manufactures the sprayer. The width is an easy fix, he said. The sprayer has individual sensors and nozzles, and the numbers of each can be chosen at the time of ordering. The physical obstacles along roadways are a bigger hurdle, but can be overcome by adding hydraulics to raise and lower the boom, adding a hinge that would allow the boom to snap backward until it clears the obstacle, or some other engineering feature, Wallander said. "There's always a way to sit down and redesign the spray bar," he explained. Six months will be used to experiment with the sprayer, and to get feedback from the operators who run the equipment. "This is still in the early stages," explained Cal Schiefferly, associate equipment engineer with Caltrans. "We need to see how the equipment actually works in the field. I don't have any concerns about its ability to spray weeds, but we need to hear back from the operators before we'll know how it's going to work and what kind of changes we'll need to make." The sprayer - called the WeedSeeker - emits thousands of bursts of light each second. Within that spectrum are a couple of wavelengths that announce the presence of chlorophyll. A sensor notes that, and triggers the appropriate nozzle. The sprayer was introduced four years ago into the agricultural market. Caltrans will use it much as California farmers do - as an alternative to spot spraying by hand. Caltrans oversees 15,000 miles of roadsides and has an annual weed control budget of $25 million. The standard program is to spray a pre-emergent herbicide on the shoulders of the road, then come back and spot spray any weeds that escape the first application. Pre-emergent herbicides are those that are applied before the weed emerges. They reside in the top inch of soil and kill weeds as the weeds germinate in the spring. However, they lose their effectiveness over time, and some escapes inevitably occur. To see the results yourself, next time you're driving on the interstate, look at the shoulder. Those few green weeds that have popped up amid the bare strip of ground are escapes.

Standard Approaches Weed control is important for fire safety, to maintain sightlines for drivers, and for aesthetics. The standard approach has been to control escapes in one of two ways:1.) Send out a truck and a single driver, who triggers the spray boom whenever he or she sees a weed. The drawbacks are that the driver's attention is distracted, and more chemical is used than is needed because the entire boom is activated while the weed has a width of only inches; and 2.) send out a truck with a driver and an employee on the front. The employee has a hand sprayer, which he or she uses to spray weeds as they occur. This is a more efficient use of chemical, but requires two salaries and is a hot and dusty job for the employee with the hand sprayer. The WeedSeeker has an additional advantage over a human spot sprayer. "When you're hand-spraying, you'll almost always put on too much chemical. It's hot and dusty out there and when you see a weed, it's human nature to want to be sure you've killed it," said Jim Beck, president of Patchen California and inventor of the WeedSeeker. The difficulty will come in determining whether the WeedSeeker's potential translates into practical benefits, said Shields. "We're approached by companies all the time," he said. "We listen to them, but the proof comes when we get the product out in the field." Shields said preliminary reports are promising. The sprayer will be moved around the state over the next six months so that different Caltrans operators can use it. The technology will work best, predicts Schiefferly, along rural stretches, where physical obstacles are rare and there can be several hundred feet between weeds. The results also will depend on another human factor familiar to anyone who is working to introduce new technology: how quickly line employees will adapt to a new idea. "Some of them will make it work; others won't," predicted Schiefferly.